Field of the Invention
This invention relates to a new polypeptide having an enhanced 1-deoxy-D-xylulose 5-phosphate synthase (DXS) activity compared to typical plant or bacteria DXS proteins. This polypeptide is responsible for a massive accumulation of terpenes in cells.
The invention also relates to transgenic plants, bacteria or yeast that express this polypeptide, and are capable of a greatly enhanced accumulation of terpenes, in comparison to plants, bacteria or yeast expressing a typical DXS gene.
The invention also relates to a method of production of terpenes by culturing transgenic plants, bacteria or yeast that express this polypeptide.
Finally the invention relates to transgenic plants that express this polypeptide, and are resistant to clomazone.
Description of the Related Art
Isoprenoids (also known as terpenoids or terpenes) are considered to be the largest family of natural products occurring in nature, with over 29 000 individual compounds identified to date. Chemically, they are extremely diverse in their structure and complexity. Isoprenoids are involved in numerous fundamental biological functions and therefore, they are essential for the normal growth and developmental processes in all living organisms. For instance, isoprenoids include eukaryotic membrane stabilizers (sterols), animal and plant hormones (steroids, retinoids, gibberellins and abscisic acid), pigments for photosynthesis (carotenoids and phytol side chain of chlorophyll), and carriers for electron transport (menaquinone, plastoquinone and ubiquinone).
Consequently, isoprenoids are a large, diverse group of complex natural products with considerable commercial interest. Isoprenoids are today mostly extracted from plants or chemically synthesized to be used as pharmaceuticals (e.g. taxol, bisabolol, and artemisinin), animal feed supplements and food colorants (various carotenoids such as lycopene and β-carotene) or flavors and fragrances (e.g. menthol, patchoulol, and nootkatone).
Isoprenoids are classified into groups according to the number of carbons they contain; the major groups of interest are monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and triterpenes (C30).
All isoprenoids are synthesized via a common metabolic precursor, isopentenyl diphosphate (IPP; C5). It was previously assumed that IPP was synthesized exclusively from mevalonate by the so-called <<mevalonate pathway>>. However, more recent investigations have shown that in eubacteria, green algae, and plants, IPP is also synthesized by a different pathway, designated the 2-C-methyl-b-erythritol-4-phosphate (MEP) pathway. Therefore, plants possess both the mevalonate and the MEP pathways, responsible respectively for the biosynthesis of IPP in the cytosol and in plastids.
The first intermediate of the MEP pathway is 1-deoxyxylulose-5-phosphate (DXP), whose biosynthesis from glyceraldehyde-3-phosphate (63P) and pyruvate is catalyzed by the thiamine-dependent enzyme 1-deoxyxylulose-5-phosphate synthase (DXS). DXS has been shown to catalyze a rate-limiting step in the formation of isoprenoids in bacteria and in plants. Indeed, in Arabidopsis thaliana and tomato (Lycopersicon esculentum), the over-expression of DXS resulted in elevated levels of plastid-derived isoprenoids like carotenoids. This is also the case in aromatic plants such as spike lavender (Lavandula latifolia), where the over-expression of DX5 led to a substantial increase in essential oil production.
Terpenoids are involved in aromas and fragrances of many plant-derived products, and, among them, monoterpenols contribute strongly to the aroma profiles of table grapes and wines. Floral flavors described as rose or lily of the valley, are related to the presence of molecules such as linalool, geraniol, nerol, alpha-terpineol or citronellol. The highest concentrations of these molecules are found in varieties of the “Muscat” group or in Gewurztraminer, leading to very characteristic aromas in these varieties. Floral flavors have appeared spontaneously in genotypes not related to the Muscat group.